In recent years, automobile users have required to maintain the beautiful appearance of a new automobile. For removing the stain of the inhibition factor, the automobile users have washed the automobile with detergent and water, wiped out water, and cleaned off or polished with water-repellent wax.
However, this work is a hard work which needs a few hours and therefore causes a lot of load to the users. Particularly, many waxes are water repellent, so that the stain is not removed because of large adhesive work in raining whether the stain is hydrophilic or hydrophobic. In addition, when the drop of water is dried, it becomes an unsightly stain in pattern of dots. Therefore, there are some cases that all pain maintenance by the users go for nothing in a day. The users require goods which decrease the load of the maintenance.
Also, the mind of environment protection increases recently. As the result, water pollution caused by the outflow of detergents and petroleum wax into rivers is feared. Some countries in Europe inhibit automobile washing at home. From such background, researches that the frequency of automobile washing by users is decreased by cleaning with raining and researches of coating or after-treatment agent which can clean the stained automobile without using the detergent have been conducted. For achieving the subject, it is suggested that it is good to decrease the adhesive work of the stain in water, that is, to increase the surface energy of the paint film for hydrophilic property (TOSO KOGAKU, vol. 31, No. 7, pages 260 to 320).
As concrete methods for giving hydrophilic property to the paint film, for example, international publication WO94/06870 discloses the coating composition comprising a specific organic coating composition and a specific organosilicate and/or a condensate thereof. The coating composition gives the paint film on which the contact angle of water is not more than 70 degree after acid treatment. And, international publication WO97/23572 discloses that the application of photocatalytic coating composition on the surface of the substrate, can give high degree of hydrophilic property.
However, the method of international publication WO94/06870 needs a long time for giving hydrophilic property to the paint film after formation of the paint film. The method can not obtain the user's satisfaction in automobile, which requires the manifestation of function immediately after buying. This point is different from structures. Since the silicate exists as pattern of spots in the inside of the paint film, there is a trend that the paint film becomes whitish by the difference of refractive index between the silicate and the binder or causes blushing phenomenon by water absorption of the silicate in the spot pattern when the paint film contacts water. It proves fatal to the automobile coating, which requires high quality appearance as goods and high durability. In addition, the lowest contact angle of water on the paint film treated with acid in Examples is 56 degree, and therefore, hydrophilic degree of the paint film is insufficient. In view of the maintenance-easy paint film having a contact angle of 30 degree or below, which can remove the hydrophobic stain such as carbon powder only by spray washing of automobile, the paint film is much lacking in hydrophilic degree.
Further, the method of international publication WO97/23572 can give hydrophilic property to the paint film in high degree by light irradiation, but is insufficient in view of uneven effect, because the vertical surface such as a door can not receive the light sufficiently and the effect may decrease or eliminate when the light irradiation is stopped in night or garage safekeeping. Since hydroxyl radical and superoxide ion generated in the photocatalytic reaction damages the organic paint film of the lower layer, the method is improper to the automobile which requires long term weathering resistance. The problem can be resolved by making regular maintenance for repainting, but the repainting maintenance is not desirable in cost because there is a possibility that maintenance cost of users is the same as prior maintenance cost or larger.
The present invention has an object to provide the coating composition which can give the paint film manifesting high degree of hydrophilic property, which has a function of cleaning the stained automobile not only by self washing with rain but also only by spray washing immediately after the formation of the paint film and further, having weathering resistance, water resistance and chemical resistance like that of prior automobile coating.
Another object of the present invention is to provide methods of coating which can give more excellent appearance to the finished article, and to provide coated articles prepared by utilizing the methods of coating.
Extensive investigations undertaken by the present inventors in order to develop the coating composition having preferable properties described above lead to a discovery that the objects can be achieved by using a stain resistant coating composition (called as the present first invention) comprising (A) a specific aliphatic sulfonic acid compound or a specific amine salt of aliphatic sulfonic acid compound, (B) a compound having in the molecule at least one functional group selected from the group consisting of carboxyl group, carboxylic acid anhydride group and carboxyl group blocked with an alkylvinyl ether compound, (C) a specific organosilicate and/or a condensate thereof, and (D) a resin having in the molecule one or more epoxy groups and/or alkoxy silyl groups, as indispensable components, and optionally (E) a dispersing component of at least one inorganic oxide sol selected from the group consisting of aluminum oxide sol, silica sol, zirconium oxide sol and antimony oxide sol and/or (F) a modified resin having a modified part derived from a specific organosilicate and/or a condensate thereof, and an acrylic resin structure part having in the molecule one or more hydroxyl groups, or both of one or more hydroxyl group and one or more epoxy groups, and a stain resistant coating composition (called as the present second invention) comprising a modified resin prepared by polymerizing a mixture of polymerizable monomers for an acrylic resin synthesis containing a hydroxyl group-containing radical polymerizable monomer or both of a hydroxyl group-containing radical polymerizable monomer and an epoxy group-containing radical polymerizable monomer, in the presence of a specific organosilicate and/or a condensate thereof, and optionally (B) a compound having in the molecule at least one functional group selected from the group consisting of carboxyl group, carboxylic acid anhydride group and carboxyl group blocked with an alkylvinyl ether compound, and/or (C) a specific organosilicate and/or a condensate thereof.